[TowerTalk] 160m Vertical

David Robbins K1TTT k1ttt at arrl.net
Mon Sep 17 16:16:08 EDT 2007

Instead of watching swr try watching for a zero in the X.  remember, the
impedance should be around 35-40 ohms so expect a minimum swr of about 1.4:1
at resonance.  

Also, what is the bottom insulator?

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of AB5MM
> Sent: Monday, September 17, 2007 16:40
> To: towertalk at contesting.com
> Subject: [TowerTalk] 160m Vertical
> Thank all of you for the answers and suggestions so far in this hair
> pulling project called "Matching at 160m Vertical".
> Larry N8KU, John KK9A, Carl KM1H, Bob W5AH, Rodger KI4NFQ, Frank W3LPL,
> Arlan N4OO, Jeff N8CC
> I need to answer a few questions:
> (1) The SWR analyzer(s) MFJ-249 and MFJ-259B.
> (2) We are also using a Eico 170 GDO.
> (3) The ground radials are located on top of the soil. I made a aluminum
> grounding buss bar as a central location for all ground radials to
> terminate at a common location. The buss bar is bolted directly to the
> tower base at around 6" above ground level.
> (4) Sweeping the tower directly at the feed point (short RG-8 pig tail)
> I do not have a dip anywhere in the 1.8 to 2.0 MHz range.
> It does show a slight dips at;
> 1.739 MHz with a swr of 3.7/1 with X=29 & R=10.
> 4.254 MHz, 4.6/1 swr  X=100 R=30
> 4.734 MHz, 4.0/1 swr  X=28 R=86
> 5.670 MHz, 3.3/1 swr  X=29 R=80
> 8.665 MHz, 2.2/1 swr  X=49 R=36
> The formula for a 1/4 wave length radiator is 234/fo. I really think
> that is for a reasonably sized wire antenna. The Rohn 25g is ~12" in
> diameter, which would make the Q a little lower (wider band width) as
> well as shift the resonance down a few kc. I think we are very close to
> the correct height, if not a little short at 120 ft. - 6 inches. Do any
> of you think the guy wires are adding a capacitive loading component? Is
> that what's throwing a wrench in the works?
> I'll sweep the tower this afternoon with the GDO to see if I can get any
> indication of resonance in or around the 160m band. The path from the
> shack to the tower is well worn now :-))
> Steve AB5MM
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